Note: Descriptions are shown in the official language in which they were submitted.
3~3L2
4~,01~ :
MULTIPOIE G~O~D F~ULT CIRC~JIT
I~TEE~UPT13R WITI~ T~IP T~VEL ADJ~TP~NT
` ~L~N
This i~entlon relates ~o ground ~ault; in~e~
rupter~ ~or personnel pro~eetion aI~d partlcularly to s~ch
in~errupters adapt~d for use in mllltipole applicakion~.
In ~en~ik e~ al U~,S. Pa~erlt 3,999~1C)3, iss~ed
Dec~m~er 21, 197&, i~ disclo~ed a multipole grouncl ~ault
circui~ breaker with inte~pting c~pability in the event
of a gro~d ~ul~ ~rom any o~e OI two or more line con-
ductors or power poles o~ ternating curren~ electrical
distribution system that ~ncludes~ ln addltion to ~he line
conductor3J a neu~ral cond~ctor that i~ gr~unded proximat~
the alternating current source~ l~eatures o~ such apparatus
are also disclosed in M~senci~ U~S~, Patent 4~01~9169
M~r¢h 29, 1977, and aanadia~ ~plication Ser~al Noi. 2465961
filed March 2, 1976 by Zal~r~ewski e~ al,.~, a~signed ~o the
present assignee O Th~ expsrience to the present ~ith such
apparatus has been generally quit~3 sati~actory. :However~
~here i~ an aspect o~ its marmer of opera~io~ that can
c~use undeslrable opera~ion under some circl~nstance~
Ground faul~ inter~pters for p~rsonnel protec~
~ion are required ~y industry standards to main~ain a trlp
2 48,018
level that is nominally 5 milliamperes, that is the current
level produced by a ground fault which causes interruption
is to be in any given device equal to 5 milliamperes plus
or minus l mil].iampere. Achievement of this ~rip level i5
readily within the capability of the apparatùs described in
the foregoing patents and application. With both poles of
a two pole ground fault circuit breake:r energized, which is
the normally expected case, a satisfactory trip level
within the standard is produced. But, with only one of the
two poles energized, it has been found by experience that
there is a tendency for the trip level to be reduced to a
lower than desirable level. That is, the amount of current
causing interruption can therefore be sQ low as to cause
-~ nuisance trippi.ng of the apparatus. It is primarily with
respect to the problem of providing an easy means of trip
level adjustment in multipole ground fault lnterrupters
that the present invention is directed.
The trip level is primarily determined by the
characteristics of the sensing amplifier and trip circuit
of the device. A given amplifier and trip circuit is
subject to possible variation in performance depending on
how it is biased. For example, a sense amplifier and trip
circuit that has been found to be very useful is that
disclosed in Engel et al ~Patent 3,852,642, `December 3,
1974, which has an advantage oE being operable on a half
wave rectified supply, as wel.l. as a full~wave rectified
supply. In the latter case, encountered in multi-pole
applications, the off-time of the amplifier :is reduced to a
minimum.
3o It is found that if a unit is designed and made
3 48,01~
to have a trip level of S.0 ma. on a full-wave supply~ that
same unit will exhibit a reduced trip level on a half-wave
supply. The amplifier for a 2-pole GE' breaker is set at
5.0 ma. assuming both poles are on. If the unusual occwrs
in ~he use of such a unit and the user forces the handle
for one pole on and the other pole off, then the ampli.fier
is seeing a half-wave rectified supply tha-t reduces the
trip level, typically about O.S ma. That is, if a unit is
tested and found to operate at a trip level in the low part
of the acceptab:le range, say 4.2 ma. with both poles ener-
gized, it could have a trip level of 3.7 ma., outside the
desired range, with only one pole energized. This inven-
tion is aimed to correct that situation.
In part, the present invention utilizes princi-
~,~, ;~s~
ples discussed in Misenick et alIPatent 4,056,837,~November
~-- l, 1977 which shows how a resistive circuit branch connected
between line and neutral conductors on opposite sides of a
differential current transformer of a GFI influences the
effective trip level of the device.
Another situation has been found in multi-pole
GFI applications which is to be improved. Where the elec-
trical system is three phase, the phase relation of the
line voltages is such as to reduce the trip level. So if a
given unit is made to exhibit a 5.0 ma. ~r trip level on
single phase operation from two poles, its trip level is
reduced if applied to a three phase system, even ;.f all
poles of the three phase system are on. An aspect of the
invention is therefore to extend the utility of GFI's for
permitting application of a single unit to either single or
multi-phase applications.
~o~
S~<I~T OF ~ ~ INVE _
In aGcordance with the present i~ntiQn, ~he
circuitry of a multipole ground fault interrupter~ ~ich
may be generally of the type as d~sc~ibed in the a~ore~
mentioned U~S~ Patents 3?999,103 and k,O15,169 and in
Canadian application Serlal ~o. 246~961 or Qf any other
: similar type of multipole ground ~au:Lt interrup~er~ i~
modi~ied by the addit~.on o~ a compen~ation network to
prevent trip le~el reduction due to ~elec~ive pole oper~
a~ion~ that is with less tharl all poles anergized. The
compen~a~ion netw~rk comprises matched impedance~, pre~
~erably resistors7 con~ected respecti~el~ to each of the
lnput hot lines and wlth the impedances ha~ng their
other ~e~inals ~on~ected ~o a con~on p~i~ fxom which
a third i~pedanceJ pre~erably also a resistor, ~ con-
nected in a circuit branc~ ex~end~ng ~hrough the core of
the di~erential curren~ ~ra~former in a dlrection ~om
the load side to the supply side ~d terml~a~ing by con-
nection with the neu~ral conductor.
This added compensation network permit~
achie~ment o~ khe desir~d 5 milli~mpere plus or minus 1
milliampere trip l~vel under conditions o~ a single pole
being energi~ed o~ the multipole apparatus ~y permitting
the trip level to be set by selection o~ the third impe-
dance~ This impedance will deter~ine the amoun~ o~ current
flowing through the circu-.Lt branch in ~he tran~former core
that ~ends to desensitize the apparatu~ and pro~ide some-
wha~ o~ an ele~ation of trip level. Xn the e~ent that
all poles are ener~i~ed~ ln a ~ingle phase s~stem then
3Q the compensation networ~ has no effect on operat~on, in-
cl~ding no e~ect on originall~intended trip level~
~3
4gJ01~
Furkhermore~ the compensakion networ~ can be
u~ed ~o pro~ide a ~ontlnuing function in ~hree phase
applications by pro~iding a d~sensitlzlng current even
with all poles on~
~ t ean be seen ~he compens~tion network of the
present inventiGn has unique fea~ures and capa~Iitie3 as
compared with the appara~us desc~ibed in khe aforementioned
U~S. patent ~,056,~37 on trip level ad~u~tment.
Further aspec~s of the arrangeme~t~ in accordan~e
with the present i~en~ion a~d ~heir operatio~ w~ll be
found by re~erence to the dra~in~ and the ensuing ~e~crip~
~ionO
Figure 1 i~ a circui~ sch~ma~ic diagram o~ an
embodime~t of the present i~entio~ in a single phase
applica~ion9 and
Figure 2 is a partial schematic diag~am o~ a
throe phase appliea~ion o~ the in~ent~on,
P~EFERRED EMBODIMENrS OF THE INVENTION
~0 Referri~g to Figure 1~ there are show~ two
power conductors Ll and L2 and a neutral conductor N
of a three~
c
2~ f~2
6 ~l~,018
wire AC power distribution system. Each of the line conduc-
tors Ll and L2 carry equal and opposite voltages such as in
a 120/240 volts single phase electrical distribution system
The neutral conductor N is grounded proximate the supply.
Within the dashed line box 8 are generally included those
elements of the apparatus that are contained within the
unit normally made and sold as a ground fault interrupter
circuit breaker which has terminals 1 through 6 provided
- for connection with the distribution system conductors that
are external to the unit. The apparatus could be contained
in an electrical wall receptacle or a portable ground fault
interrupter unit as well as in a circuit breaker intended
to be mounted in the load center o~ a distribut.ion system.
The conductors L1, L2 and N pass through a mag-
netic core 10 of a differential current transformer prefer-
ably as single ~urn primary windings. The core also has a
~: secondary sensing winding 12 wound on the core in normally
a plurality of turns. The leads of the sensing winding 12
go to a sensing amplifier and trip circuit 14. The ampli-
fier and trip circuit 14 responds to signals developed by
the sensing winding 12 as a result o~ current imbalances in
the primary conductors that are indicative of a ground
fault that may be harmful, such as a line to ground resis-
tive path as indicated at 9. If such an imbalance occurs,
the trip circuit l.4 causes the opening of circuit brealcer
mechanisms 17 and 18 and resulting protection for an indivi-
dual who may he in the ground path 9 from the line conductor.
Solenoid trip coils 15 and 16 are individually provided in
association with breaker contacts 17 and 18 with one end of
each connected to respective line conductors Ll and L2.
7 4~,01~
The mechanisms are preferably connected together (dashed
lin~ 19) for concurren~ operakion of the bre~;er con~acts
on each of the line conductvræO ~he other end of the trip
coils lS and 16 are con~ecked to respective ~ener diodes
21 and 22 which are poled in the same direction betwee~
the respective lines Ll and L2 and a common lead to the
trip circuit 14~ Okher aspects wi~h respect ko khe supp~
o~ power ko the trip circuit, including lead 26, zener
; diode 2~ and capacitor 30~ and the manner of operation
and chara~ter o~ suita~le trip circuits are ~iscussed in
re~erred-~o U~S~ Patents ~015,169 and 39~2~642~
In accordance with pre~erred practice~ the
apparatus comprises a grounded neutral transformer core
32 with a primary winding ~4 that is connecked through
respective di~erenk valued resistors Rl and R2 to ~he
line conductors Ll and L2 and who~e seco~dary is ~he
neutral conductor N~ The purpose and na~ure o~ operation
o~ the grounded neutral ~ransformer and its connection are
descrlbed more ~ully in the a~orementioned Canadlan
applicat~on Serial No. 246~961~
The appara~us also include~ a test circuit
branch 36 connected bet~een a point on Ll on the load
side o~ the d~fferential trans~ormer 10 and a poi~t on
the line s~de o~ the pr~mary wi~ding 34 of the g~ounded
neutral kransformer~ This branch includes a manually-
operable s~tch 3~ and a resistor 40 ~or establishing a
curre~t ~low to check the operabllit~ o~ both t~e dif
~erential current trarlsformer 10 and the grounded neutral
trans~ormer 32~ ~urther description o~ this portion of
the apparatus is in U~S~ Paten~ ~ov 37930,1~7~issued
Decem~er 30~ 1975, to M~sencikO
The porkions o~ the apparatus thus ~ar desc~ibed
j~!
4;2
~:!Ol~
are merely exemplary of a pre~erred embodiment in ~hich
the present in~ention is used. The i~entio~ pertains
most directly to a compensation ~et~rk 50 that has
individual matched resistors R3 and R~ respecti~ely con~
nected to each o~ the line conductors Ll and L2 on the
su~ply side of the ~rans~o~mer lOo me resistors R3 and
R~ are connected at t~eir other ends to a co~mon po~nt
51~ The reason for hav~g these resistors or other
current deYeloping impedances in the ind~vid~al circuit
br~nches to the lîne conduc~or~ is because at some time
a user mlght deenergize one pole o~ the multi~pol~e
breaker and produce a reduction in trip le~el o~ trip
circuit 14 tha~ has a charact~ristic difference in per-
formance when its bias changes from ~ull-wa~e rectified,
as produced by both poles being on~ to hal~-wave recti-
fied9 with one pole o~
The res~stors ~3 and R~ are clo~ely matched~
~uch as within abou~ 1~, to ensure tha~ the~ do not
modify ~he trip level o~ the apparatus when both power
poles Ll and L2 are energizedO ~3 and R4 ara also o~
apprec~able lmpedance val~e9 such as greatar than 100~000
ohms each7 to maintain an ~dequa~e isola~ion between Ll
and L2~ Prom the common poin~ o~ R3 and N~ there is
connected anokher re~istor R5 who~e other end is con-
nected to the neutr~l conductor N by a conductor 52 that
extends around the core to the supply side of ~he tran3
~o~merO
~ lth both poles Ll and L2 energi~ed, that is
carrying their normal~y~intended current and voltage~
there is zero current through the Compensa~iQn net~ork
because the currents developed by R3 and R4 are equal
and opposite and c~lcel each other at common point 51
~ence9 when both
.~ .,.~ .~.;
A ~ i
9 48,018
poles are energized, the compensation network 50 produces
no effect on the operation of the apparatus.
When only one of the power poles Ll or L2 is
energized, there is a net current flow through the compensa-
tion network and a desensitizlng current ID flows through
conductor 52 that reduces the sensitivity of the apparatus.
The desensitizing current ID equals the voltage on the
energized pole divided by the sum of the resistor R3 or R4
connected to that pole plus RS; i.e.,
10Volta e (Ll) Volta~e (L2).
R3--g--F~j or R~-~ RS ~~~~
This amount of current desensitizes the apparatus because
it requires that an additional ground fault current of that
amount, in addition to the fault current otherwise required,
be drawn to cause the apparatus to be actuated.
~ or example, typical ac-tual values encountered in
practice are:
Trip level with both poles energized 5 ma. + 1
Trip level with only 1 pole energized,
without compensation 4.5 ma. + 1
20Resistor values for compensa-tion in a
120/240 v. system:
R3 120k ohms.
R4 120k ohms.
R5 lOk ohms.
The invention is also applicable to ground fault
interrupters of more than one phase. For example, applica-
tion of the .invention has been made to three phase appara
tus having nom:inal voltages s-wch as 120/208 volts.
Figure 2 shows a representative connection of a
3 ground fault circuit breaker 8, as in Figure 1, to a 3-
phase wye distribution system. Here the compensation
. - .
lQ ~8,018
: network 50 in the uni.t 8 will supply a densi.tizing current
ID in branch 52 throughout operation when either or both Ll
and L2 are on. In this arrangemcnt the third phase lead L3
goes to another breaker and does not influence operation of
the unit 8.
As a result of the practice of the invention in
accordance with the foregoing description, it will be seen
that it provides a way to avoi.d overly-sens-.itizing the
apparatus as a result of only one pole of the multipole
system being energized while fully preserving the capabil-
ity o~ the apparatus when all poles are energized, in
either a single phase system or a three-phase system.
Thus, there is achieved through a relatively simple exped-
ient not unduly complicating the apparatus or its ability
to be made economically and compactly, a system that pro-
vides a uniorm trip level under a variety of conditions.
